Controlled Electrolytic Metallic Materials for  Wellbore Sealing and Strengthening

ABSTRACT

Contacting the wellbore with a fluid composition and forming a metallic powder barrier at or near the tip of a fracture extending from the wellbore into a subterranean formation may strengthen a wellbore. The fluid composition may include a base fluid and a metallic powder having a plurality of metallic powder particles. The base fluid may include a drilling fluid, a completion fluid, a servicing fluid, a fracturing fluid, and mixtures thereof. The metallic powder particles may have a particle core and a metallic coating layer. The particle core may include a core material selected, such as magnesium, zinc, aluminum, manganese, vanadium, chromium, molybdenum, iron, cobalt, silicon, nitride, tungsten, and a combination thereof. The metallic coating layer may be disposed on the particle core thereby forming a metallic powder particle. The metallic powder particles may be configured for solid-state sintering to one another to form the metallic particle compacts.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Provisional Patent ApplicationNo. 61/695,474 filed Aug. 31, 2012, which is incorporated by referenceherein in its entirety.

TECHNICAL FIELD

The present invention relates to sealing and strengthening a wellbore bycontacting the wellbore with a fluid composition and forming a metallicpowder barrier at or near the tip of a fracture extending from thewellbore into a subterranean formation.

BACKGROUND

Drilling fluids used in the drilling of subterranean oil and gas wellsalong with other drilling fluid applications and drilling procedures areknown. In rotary drilling there are a variety of functions andcharacteristics that are expected of drilling fluids, also known asdrilling muds, or simply “muds”. The functions of a drilling fluidinclude, but are not necessarily limited to, cooling and lubricating thebit, lubricating the drill pipe, carrying the cuttings and othermaterials from the hole to the surface, and exerting a hydrostaticpressure against the borehole wall to prevent the flow of fluids fromthe surrounding formation into the borehole.

Drilling fluids are typically classified according to their base fluid.In water-based muds, solid particles are suspended in water or brine.Oil can be emulsified in the water, which is the continuous phase.Brine-based drilling fluids, of course are a water-based mud (WBM) inwhich the aqueous component is brine. Oil-based muds (OBM) are theopposite or inverse. Solid particles are suspended in oil, and water orbrine is emulsified in the oil and therefore the oil is the continuousphase. Oil-based muds can be either all-oil based or water-in-oilmacroemulsions, which are also called invert emulsions. In oil-basedmud, the oil may consist of any oil that may include, but is not limitedto, diesel, mineral oil, esters, or alpha-olefins. OBMs as definedherein also include synthetic-based fluids or muds (SBMs). SBMs ofteninclude, but are not necessarily limited to, olefin oligomers ofethylene, esters made from vegetable fatty acids and alcohols, ethersand polyethers made from alcohols and polyalcohols, paraffinic, oraromatic, hydrocarbons alkyl benzenes, terpenes and other naturalproducts and mixtures of these types. OBMs and SBMs are also sometimescollectively referred to as “non-aqueous fluids” (NAFs).

Damage to a reservoir is particularly harmful if it occurs whiledrilling through the pay zone or the zone believed to hold recoverableoil or gas. In order to minimize such damage, a drill-in fluid may bepumped through the drill pipe while drilling through the pay zone.

Another type of fluid used in oil and gas wells is a completion fluid. Acompletion fluid is pumped down a well after drilling operations arecompleted and during the completion phase. Drilling mud typically isremoved or displaced from the well using a completion fluid, which maybe a clear brine. Then, the equipment required to produce fluids to thesurface is installed in the well. A completion fluid must havesufficient density to maintain a differential pressure with thewellbore, which controls the well.

When drilling through a rock formation, mud may be lost into theformation through fractures (small or large fissures) of the formation.In other instances, fractures may be induced while drilling, such as inthe case of drilling with a high overbalanced pressure through depletedsands. With both types of fractures, i.e. naturally-occurring orinduced, severe fluid loss may occur, especially when drilling with anoil-based drilling mud. Examples of fluids that may be lost include, butare not limited to water or oil from drilling and completion fluids,typically used for downhole purposes, and the like. Another example iswater invasion into shale formations, which may weaken the wellborecausing stability problems, such as a hole collapse.

Solid particles from the aforementioned types of fluids may physicallyplug or bridge across flowpaths at or near the fracture tip of theporous formation. Chemical reactions between the drilling fluid and theformation rock and fluids may precipitate solids or semisolids to plugpore spaces. It will also be understood that the drilling fluid, e.g.oil-based mud, is deposited and concentrated at the borehole face andpartially inside the formation. However, the solid particles plugging orbridging across the formation may only be desirable for a temporaryamount of time because the plugging can also cause a reduction ofhydrocarbon production. Many operators are interested in improvingformation clean up and removing the formed plugging material afterdrilling into reservoirs.

It would be advantageous to design a fluid composition havingpotentially degradable particles where the degradable particles may sealthe wellbore or form a plug at or near the fracture tip for purposes ofstrengthening the wellbore and allow for the degradation of the plug ifso desired.

SUMMARY

There is provided, in one form, a method for sealing and/orstrengthening a wellbore. A fluid composition may contact the wellborewhere the fluid composition includes a fluid and a metallic powderhaving a plurality of metallic powder particles. The metallic powder mayform a metallic powder barrier at or near the tip of a fractureextending from the wellbore into a subterranean formation. The fluid maybe a drilling fluid, a completion fluid, a servicing fluid, a fracturingfluid, and mixtures thereof. Each metallic powder particle may include aparticle core, and a metallic coating layer disposed on the particlecore. The particle core may have or include a core material with amelting temperature (T_(p)), and the core material may be or includemagnesium, zinc, aluminum, manganese, vanadium, chromium, molybdenum,iron, cobalt, silicon, nitride, tungsten, and a combination thereof. Themetallic coating layer disposed on the particle core may include ametallic coating material having a melting temperature (T_(c)).

In an alternative non-limiting embodiment, the metallic powder particlesdescribed above may be configured for solid-state sintering to oneanother at a predetermined sintering temperature (T_(S)) where T_(S) isless than T_(P) and T_(C) to form a metallic particle compact. Themetallic powder particles and/or the metallic particle compacts maydegrade after a predetermined condition including, but not necessarilylimited to, a temperature change, the presence of an acid, an amount oftime, or a combination thereof. A metallic powder barrier that includesthe metallic powder particles may form at or near the tip of thefracture that may reduce additional growth of the fracture as comparedto a wellbore contacted with a fluid composition absent the metallicpowder.

The metallic powder barrier formed from the metallic powder appears tocontrol the fracture size and strengthen the wellbore.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a non-limiting, schematic illustration of three types ofmetallic powder particles with degradable portions thereof.

It will be appreciated that the various structures and parts thereofschematically shown in FIG. 1 are not necessarily to scale or proportionsince many proportions and features have been exaggerated for clarityand illustration.

DETAILED DESCRIPTION

A method has been discovered for strengthening and sealing a wellborethat involves the use of at least partially degradable metallic powderparticles blended with a base fluid, such as but not necessarily limitedto a drilling fluid, a completion fluid, a servicing fluid, a fracturingfluid, and mixtures thereof to form a fluid composition. Once a fractureis induced within a subterranean reservoir, various fluids may be lostinto the formation, also termed ‘lost circulation’ of fluid.

To prevent loss of water or other fluids into the formation, themetallic powder particles may be carried into these fractures and act asproppants and thereby strengthen the wellbore by forming a stress cagearound the wellbore. The concentration of the metallic powder within thefluid composition may range from about 0.05 wt % independently to about10 wt %, alternatively from about 0.05 wt % independently to about 3 wt%. When the term “independently” is used herein with respect to aparameter range, it is to be understood that all lower thresholds may beused together with all upper thresholds to form suitable and acceptablealternative ranges. The fluid composition may be pumped into thewellbore to form a metallic powder barrier at or near the tip of afracture extending from the wellbore into a subterranean formation.

‘Metallic powder barrier’ is defined herein to be a material intended toform a blockage or block passage of a fluid into or out of the wellboreand/or formation, such as but not limited to, a plug, a sealant, abridging material, and combinations thereof. Such a barrier may beuseful on small scale to block pore space of a formation, or on a largerscale to form a plug and create multiple zones within a wellbore. Themetallic powder barrier formed may reduce additional growth of thefracture as compared to contacting the wellbore with a fluid compositionabsent the metallic powder. The metallic powder barrier may also reducethe amount of fluid lost in the formation. In one non-limitingembodiment, the metallic powder barrier may form a seal on the wellboreto prevent solid and fluid going from or into the formation and/orprevent pressure transmission.

The degradable metallic powder particles and/or metallic particlecompacts may be designed to be pumpable along with the base fluid. Withtime, these metallic powder particles and/or metallic particle compactswill either degrade partially or completely in downhole formation water,fracturing fluid (i.e. mixture of water and/or brine), other fluids, orother conditions. Some of these metallic powder particles and/ormetallic particle compacts may degrade in hydrocarbons if thehydrocarbons contain H₂S, CO₂, and other acid gases that causedegradation of the materials. Oxides, nitrides, carbides, intermetallicsor ceramic coatings that are partially or fully resistant of thesedissolvable metallic powder particles and/or metallic particle compactsmay be dissolved with a second fluid, such as an acid or brine-basedfluids. This allows for a metallic powder barrier to form at or near thefracture tip for a period of time that the metallic powder barrier isneeded, and then the degradable metallic powder particles and/ormetallic particle compacts within the metallic powder barrier may bedegraded according to pre-determined conditions or once the metallicpowder barrier is no longer needed. By “at or near” is meant within afew inches, e.g. about 2 inches independently to about 4 inches from thetip of the fracture, or alternatively, less than 1 inch from the tip ofthe fracture.

In a non-limiting embodiment, the metallic powder particles may beoil-wet from the oil-based muds. A surfactant may contact the metallicpowder particles and/or formed metallic powder barrier to change atleast a portion of the metallic powder particles from oil-wet towater-wet; alternatively, a mesophase fluid may be injected into thewellbore to change the metallic powder particles from oil-wet towater-wet. More specifically, the surfactant (in the absence of amesophase fluid) or the mesophase fluid may reverse the wettability,remove and/or minimize the metallic powder barrier formed from themetallic powder particles at or near the fracture tip. Mesophase fluidsare defined herein as selected from the group of a miniemulsion, ananoemulsion, macroemulsion or a microemulsion in equilibrium withexcess oil or water or both (Winsor III), a single-phase microemulsion(Winsor IV) as defined by U.S. Pat. No. 8,235,120, which is incorporatedherein by reference.

In an alternative non-limiting embodiment, the metallic powder particlesmay be water-wet from the water-based muds. A surfactant may contact themetallic powder particles and/or formed metallic powder barrier tochange at least a portion of the metallic powder particles fromwater-wet to oil-wet; alternatively, a mesophase fluid may be injectedinto the wellbore to change the metallic powder particles from water-wetto oil-wet. More specifically, the surfactant (in the absence of amesophase fluid) or the mesophase fluid may reverse the wettability,remove and/or minimize the metallic powder barrier formed from themetallic powder particles at or near the fracture tip.

In this instance, the metallic powder particles may be oil-wet (ornon-polar), so the mesophase fluid may be water-continuous. Mesophasefluids also include collections of components that make these emulsions.These mesophase fluids may be formed either prior to introduction into awellbore or formed in situ. That is, it is not necessary to completelyform the mesophase fluid (e.g. microemulsion) on the surface and pump itdownhole. The in situ mesophase fluid (e.g. microemulsion, nanoemulsion,etc.) may be formed when at least one surfactant and a polar phase(usually, but not limited to water or brine) contacts the non-polarmetallic powder particles and solubilizes the non-polar materialthereon. Such mesophase fluids may also be introduced as pills to carryout the same function.

The mesophase fluid may include at least one surfactant, an oil-basedfluid, an aqueous-based fluid, and an optional co-surfactant. Thesurfactant may be or include, but is not limited to an extended chainsurfactant, a non-extended chain surfactant, a co-surfactant, andcombinations thereof. The surfactant may be or include, but is notlimited to non-ionic, anionic, cationic, amphoteric surfactants,extended chain surfactants, and combinations thereof. Suitable nonionicsurfactants include, but are not necessarily limited to, alkylpolyglycosides, sorbitan esters, polyglycol esters, methyl glucosideesters, alcohol ethoxylates or alkylphenol ethoxylates. Suitable anionicsurfactants include, but are not necessarily limited to, alkali metalalkyl sulfates, alkyl or alkylaryl sulfonates, linear or branched alkylether sulfates and sulfonates, alcohol polypropoxylated and/orpolyethoxylated sulfates, alkyl or alkylaryl disulfonates, alkyldisulfates, alkyl sulphosuccinates, alkyl ether sulfates, linear andbranched ether sulfates, and mixtures thereof. Suitable cationicsurfactants include, but are not necessarily limited to, arginine methylesters, alkanolamines and alkylenediamides.

The optional co-surfactant may be a surface-active substance, such asbut not limited to, mono or poly-alcohols, low molecular weight organicacids or amines, polyethylene glycol, low ethoxylation solvents andmixtures thereof.

Once the metallic powder particles are water-wet, the second fluid maybe an almost neutral fluid (‘almost neutral’ is defined herein to mean apH ranging from about 6.5 to about 7.5, e.g. water) and injected intothe wellbore to dissolve the metallic powder particles. Although anacidic solution (e.g. a fluid having a pH less than about 6.5) maydissolve the metallic powder particles quicker than an almost neutralfluid, the acidic solution may corrode the well equipment downhole. Forexample, the metallic powder barrier formed from the powder particlesmay be used to aid in completion of a well; use of an acidic solutionwould corrode and/or dissolve the completion equipment for the finishedwell. Thus, depending on the use of the metallic powder particles andthe metallic powder barrier formed therefrom, one skilled in the artmust assess whether to use a second fluid that is acidic or almostneutral.

The degradable portions of the metallic powder particles and/or metallicparticle compacts may be lightweight, high-strength and have selectablyand controllably degradable materials. Fully-dense, sintered metallicparticle compacts may be formed from coated metallic powder particleshaving lightweight particle cores. A coating may be formed on theparticle core having at least one layer, alternatively from about 1layer independently to about 10 layers depending on the thickness ofeach layer. The powder particle core may be or include anelectrochemically-active (e.g. having relatively higher standardoxidation potentials), lightweight, and/or high-strength material.

The powder particles may degrade over a period of time ranging fromabout 0.5 hours independently to about 4 weeks, alternatively from about10 minutes independently to about 2 weeks, or from about 5 minutesindependently to about 24 hours.

These metallic powder particles and/or metallic particle compactsprovide a unique and advantageous combination of mechanical strengthproperties, such as compression and shear strength, low density andselectable and controllable corrosion properties, particularly rapid andcontrolled dissolution in various wellbore fluids, and combinationsthereof. For example, the particle core and coating layers of thesemetallic powder particles may be selected to provide sintered metallicparticle compacts suitable for use as high strength engineered materialshaving a compressive strength and shear strength comparable to variousother engineered materials, including carbon, stainless and alloysteels, but which also have a low density comparable to variouspolymers, elastomers, low-density porous ceramics and compositematerials.

The selectable and controllable degradation or disposal characteristicsdescribed may also allow the dimensional stability and strength ofmaterials to be maintained until the metallic powder particles and/ormetallic particle compacts are no longer needed. In one non-limitingexample, it may be beneficial to degrade the metallic powder particlesat or near the fracture tip prior to producing the well to allow for thewell to be produced at full capacity. Once the metallic powder barrierhaving the metallic particles is no longer needed, a condition may bechanged to promote the degrading of the metallic particles, such as butnot limited to a predetermined environmental condition, such as awellbore condition, including but not necessarily limited to wellborefluid temperature, pressure or pH value, salt or brine composition, etc.The degrading of the metallic powder particles may occur by a method,such as but not limited to dissolving the metallic powder particles,degrading the metallic powder particles, corroding the metallic powderparticles, melting the metallic powder particles, and combinationsthereof.

As yet another example, these metallic powder particles and/or metallicparticle compacts may be configured to provide a selectable andcontrollable degradation, disintegration or disposal in response to achange in an environmental condition. An example of an environmentalcondition may include, but is not necessarily limited to, a transitionfrom a very low dissolution rate to a very rapid dissolution rate inresponse to a change in a property or condition of a wellbore proximatean article formed from the metallic particle compact, including aproperty change in a wellbore fluid that is in contact with the metallicpowder particles and/or metallic particle compacts. Such propertychanges may be or include, but are not necessarily limited to atemperature change, the presence of an acid, an amount of time, andcombinations thereof.

In one non-limiting embodiment, these degradable powder particles may becalled controlled electrolytic metallics (CEM) particles. Methods forusing these metallic powder particles and/or metallic particle compactsare described further below, as well as in U.S. patent application Ser.No. 12/633,686 entitled COATED METALLIC POWDER AND METHOD OF MAKING THESAME, filed Dec. 8, 2009, which is herein incorporated by reference inits entirety.

Magnesium or other reactive materials could be used in the powders tomake the degradable metal portions, for instance, aluminum, zinc,manganese, molybdenum, tungsten, copper, iron, calcium, cobalt,tantalum, rhenium, nickel, silicon, rare earth elements, and alloysthereof and combinations thereof. As used herein, rare earth elementsinclude Sc, Y; lanthanide series elements, including La, Ce, Pr, Nd, Pm,Sm, Eu, Gd, Te, Dy, Ho, Er, Tm, or Lu; or actinide series elements,including Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Bk, Cf, Es, Fm, Md, orNo; or a combination of rare earth elements.

These metals may be used as pure metals or in any combination with oneanother, including various alloy combinations, such as amalgams and/orother physical combinations of these materials, including binary,tertiary, or quaternary alloys of these materials. Nanoscale metallicand/or non-metallic coatings could be applied to these electrochemicallyactive metallic powder particles and/or metallic particle compacts tofurther strengthen the material and to provide a means to accelerate ordecelerate the degrading rate.

Degradable enhancement additives include, but are not necessarilylimited to, magnesium, aluminum, nickel, iron, cobalt, copper, tungsten,rare earth elements, and alloys thereof and combinations thereof. Itwill be observed that some elements are common to both lists, that is,those metals which can form degradable metals and degradable metalcompacts and those which can enhance such metals and/or compacts. Thefunction of the metals, alloys or combinations depends upon what metalor alloy is selected as the major particle core first.

The relative degradable rate depends on the value of the standardpotential of the additive or coating relative to that of the particlecore. For instance, to make a relatively more slowly degrading particlecore, the coating composition needs to have a lower standard potentialthan that of the particle core. An aluminum particle core with amagnesium coating is a suitable example. Or, to make this particle coredissolve faster, the standard potential of the particle core needs to belower than that of the coating. A non-limiting example of the lattersituation would be a magnesium particle core with a nickel coating.

These electrochemically active metals or metals with nanoscale coatingsmay be degraded by a number of common wellbore fluids, including anynumber of ionic fluids or highly polar fluids. Non-limiting examples ofsuch fluids include, but are not limited to, sodium chloride (NaCl),potassium chloride (KCl), hydrochloric acid (HCl), calcium chloride(CaCl₂), sodium bromide (NaBr), calcium bromide (CaBr₂), zinc bromide(ZnBr₂), sodium formate, potassium formate, or cesium formate.

Alternatively, relatively non-degradable metallic powder particles (e.g.a ceramic portion) may be designed to where only the coating of eachparticle degrades in a downhole environment, while the rest of themetallic powder particle remains in place as part of the barrier at ornear the tip of the fracture. For instance, these non-degradablemetallic powder particles include high strength intermetallic particlesor ceramic particles of oxides, nitrides, carbides, or specifically MgOin a non-limiting example. The metallic powder particles could be solidor hollow. The degradable coatings include, but are not limited to, thereactive metals with corrosion enhancement coatings mentioned above.

It will be appreciated that in the embodiment where there is adegradable coating over all or a majority of a degradable particle core,there may be applications where the coating should be relatively moreeasily degraded than the particle core, and other applications where theparticle core is relatively more easily degraded than the coating.Indeed, multiple coatings over a particle core may be used to providefurther control over the degradation of the metallic powder particlesand/or metallic particle compacts. Combinations of different fluids andmetallic powder particles and/or metallic particle compacts withdifferent layers or portions that degrade at different rates willprovide many ways to design and control the formed metallic powderbarrier at or near the fracture tip depending on the desired wellborestrengthening properties, the length of time desired for a formedbarrier, etc.

The dissolvable metallic powder particles and/or metallic particlecompacts may be spherical, elongated, rod-like or another geometricshape. In another non-limiting embodiment, they may be flake or granularin shape to reduce fluid losses to the formation. One non-limitingexample of the flake shape is SOLUFLAKE™ from Baker Hughes.

The dissolvable metallic powder cores and/or metallic particle compactsformed from the metallic powder particles may be either uncoated orcoated. Uncoated particle cores may be reactive metals such asmagnesium, aluminum, zinc, manganese or their alloys, or metals withdegradable enhancement additives included in the particle core. Coatedparticles may have a particle core and at least one metallic coatinglayer. The particle core of a coated powder particle may be of metalssuch as magnesium, zinc, aluminum, manganese, vanadium, chromium,molybdenum, iron, cobalt, silicon, nitride, tungsten, and combinationsthereof.

The metallic coating material may be or include, but is not limited to,Al, Zn, Mn, Mg, Mo, W, Cu, Fe, Si, Ca, Co, Ta, Re, Ni, an oxide thereof,a carbide thereof, a nitride thereof, and a combination of any of theaforementioned materials. The metallic coating material may be adifferent chemical composition than the chemical composition of theparticle core. The metallic coating layer could be such that itaccelerates or decelerates the degradation of the metallic powderparticle. These metallic powder particles could be such that theydegrade either partially or completely over a period of time. Thedegradation rate may be controlled by the composition of the base fluid,such as but not limited to a drilling fluid, a completion fluid, aservicing fluid, a fracturing fluid, and mixtures thereof.

In a non-limiting embodiment, the core material may be Mg—Zn, Mg—Al,Mg—Mn, Mg—Zn—Y and combinations thereof. When the core material is anMg—Al—X alloy, the X may be or include Zn, Mn, Si, Ca, Y, andcombinations thereof. Additionally, the Mg—Al—X alloy may be up to about85 wt % of Mg, up to about 15 wt % Al, and up to about 5 wt % X.

In an alternative procedure, it is conceived that these degradablemetallic powder particles and/or metallic particle compacts may bedesigned so that a stimulation or second fluid triggers the degradationof the powder particle compacts and/or powder particles. After themetallic powder barrier has formed at or near the fracture, a subsequentdosing of a second fluid, different from the base fluid initially usedto deliver the degradable metallic powder particles and/or metallicparticle compacts into the wellbore, will trigger the dissolution of thedegradable particle phase or degradable particle compact phase. Theadditional stimulation fluid treatments may include an acid or brine orseawater, heated water or steam, or even fresh water—something thatprovides chemical and/or physical stimuli for triggering the dissolvablematerial to actually dissolve or degrade. The acid may be a mineral acid(where examples include, but are not necessarily limited to HCl, H₂SO₄,H₂PO₄, HF, and the like), and/or an organic acid (where examplesinclude, but are not necessarily limited to acetic acid, formic acid,fumaric acid, succinic acid, glutaric acid, adipic acid, citric acid,and the like). In another embodiment, the acid or brine may be theinternal phase of an emulsion stimulation of a cleanup fluid.

The size of the metallic powder particle may range from about 25 nmindependently to about 5000 μm, alternatively from about 100 nmindependently to about 750 μm. For a coated powder particle, i.e. onehaving a powder particle core and a powder particle coating, theparticle core may have a diameter ranging from about 1 nm independentlyto about 300 μm, alternatively from about 50 nm to about 500 μm. Themetallic coating layer disposed on the particle core may have a meltingtemperature (Tc). The thickness of the metallic coating layer may rangefrom about 25 nm independently to about 2500 nm, or from about 100 nmindependently to about 500 nm. The metallic powder particles may beconfigured for solid-state sintering to one another at a predeterminedsintering temperature (Ts) where Ts is less than Tp and Tc to form ametallic particle compact. The size of the metallic particle compactranges from about 500 μm independently to about 20 cm.

The invention will now be illustrated with respect to certain examples,which are not intended to limit the invention in any way but simply tofurther illustrate it in certain specific embodiments.

Shown in FIG. 1 is one version of a metallic powder particle 12 that iscompletely degradable, and an alternate embodiment of a metallic powderparticle 14 that has a portion 16 that is degradable at a first rate,and a portion 18 that is degradable at a second rate. In the particular,alternative embodiment of metallic powder particle 14 shown in FIG. 1,metallic powder particle 14 may have a generally central particle core18 that is relatively more slowly degradable compared to portion 16,which is relatively more rapidly degradable and is a relatively uniformcoating over the generally central particle core 18. It should beunderstood that the rates of degradation between portion 16 and portion18 may be reversed. In another non-limiting embodiment, portion 18 isessentially not degradable in the process. However, it will beappreciated that metallic powder particle 14 may have otherconfigurations, for example degradable portion 16 may not be uniformlyapplied over generally central particle core 18.

These coatings may be formed by any acceptable method known in the artand suitable methods include, but are not necessarily limited to,chemical vapor deposition (CVD) including fluidized bed chemical vapordeposition (FBCVD), as well as physical vapor deposition, laser-induceddeposition and the like, as well as sintering and/or compaction. Inanother non-limiting version, the particle may be formed of twoapproximately equal, or even unequal, hemispheres, one of which is arelatively insoluble portion 18 and the other of which is a relativedissolvable portion.

Also shown in FIG. 1 is a different embodiment of a metallic particlecompact 40, which may have powder particle cores 36 and a thin metalliccoating layer 38 thereon. Such metallic particle compacts 40 do notnecessarily have a metallic coating layer 38 over the entire metallicparticle compact 40. In a non-limiting instance, note that powderparticle core 36 on the right side of metallic particle compact 40 isnot covered by coating 38. Metallic particle compacts 40 may be reducedin size or degraded uniformly. In an alternative non-limiting embodimentof a metallic particle compact, at least two of the metallic powderparticles 12, 14, 40, and combinations thereof, may be sintered togetherto form a metallic particle compact.

In a different non-limiting embodiment, the particles of FIG. 1 may beengineered to have increased strength, at least up until the powderparticles begin to degrade. In a non-limiting example, the portion 16may be ceramic (e.g. an inorganic, nonmetallic material) and the portion18 may be metal.

It will be further understood that although metallic powder particles 12and 14 are shown as spheres, they may be other shapes including, but notnecessarily limited to, irregular rod-like, acicular, dendritic, flake,nodular, irregular, and/or porous. In another non-limiting version, themetallic powder particle may be hollow or porous. For example, themetallic powder particle may only have a coating but not a powderparticle core.

In another non-restrictive embodiment, the degradable portions ofmetallic powder particles 12 and 14 are made from a degradable metalsintered and/or compacted from a metallic composite powder comprising aplurality of metallic powder particles. These smaller powder particlesare not to be confused with metallic powder particles 12 and 14. Eachmetallic powder particle may comprise a particle core, where theparticle core comprises a core material comprising Mg, Al, Zn or Mn, ora combination thereof, having a melting temperature (T_(P)). The powderparticle may additionally comprise a metallic coating layer disposed onthe powder particle core and comprising a metallic coating materialhaving a melting temperature (T_(C)), wherein the powder particles areconfigured for solid-state sintering to one another at a predeterminedsintering temperature (T_(S)), and T_(S) is less than T_(P) and T_(C).Alternatively, T_(S) is slightly higher that T_(P) and T_(C) forlocalized micro-liquid state sintering, By “slightly higher” is meantabout 10 to about 50° C. higher than the lowest melting point of all thephases involved in the material for localized micro-liquid sintering.

There are at least three different temperatures involved: T_(P) for theparticle core, T_(C) for the coating, and a third one T_(PC) for thebinary phase of P and C. T_(PC) is normally the lowest temperature amongthe three. In a non-limiting example, for a Mg particle with an Aluminumcoating, according to a Mg—Al phase diagram, T_(P)=650° C., T_(C)=660°C. and T_(PC)=437 to <650° C. depending on wt % ratio of the Mg—Alsystem. Therefore, for completed solid-state sintering, thepredetermined process temperature needs to be less than T_(PC). Formicro-liquid phase sintering at the core-coating interface, thetemperature may be 10-50 degree C. higher than T_(PC) but less thanT_(P) and T_(C). A temperature higher than T_(P) or T_(C) may be toomuch, causing macro melting and destroying the coating structure.

The proportion of base fluid may be greater than that of completelydegradable metallic powder particle 12. In one non-limiting embodiment,the proportion of degradable particles within the total fluidcomposition may range from about 0.05 wt % independently to about 10 wt%, alternatively from about 0.05 wt % independently to about 3 wt %.

The completely dissolvable metallic powder particle 12 need not be thesame or approximately the same size as the metallic powder particle 14.In one non-limiting embodiment, average particle size of the metallicpowder particle 12 may range from about 100 nm independently to about100 microns, alternatively from about 100 nm independently to about 1micron.

After placement of the metallic powder barrier, at least a portion ofthe degradable metallic powder particle 12 may be degraded and removedtherefrom, which thereby reduces the size of the barrier. This may bebeneficial when it is desirable to have a barrier of varying sizes overa period of time, or alternatively it may be beneficial to degrade themetallic powder particles once the barrier is no longer needed. Thesecond fluid may degrade the metallic powder particles of the barrier.“Second fluid” is defined herein to mean any fluid added into thewellbore after the fluid formulation has been pumped into the wellbore,which may include but is not necessarily limited to a fluid that is thesame base fluid as the first fluid but has been altered for purposes ofdegrading the particles.

The second fluid may contain corrosive material, such as select typesand amounts of acids and salts, to control the rate of degradation ofthe particles. In another embodiment, the fluid formulation thatintroduced the metallic powder particles into the fracture may beremoved or displaced, and subsequently a second fluid may be introducedto degrade the metallic powder particles 12. This second fluid maysuitably be, but is not necessarily limited to, fresh water, brines,acids, hydrocarbons, emulsions, and combinations thereof so long as itis designed to dissolve all or at least a portion of the dissolvablemetallic powder particles 12. While all of the metallic powder particles12 may be removed, as a practical matter, in an alternate embodiment, itmay not be possible to contact and degrade all of the dissolvablemetallic powder particles 12 with the subsequent fluid and thus removeor degrade all of them. In one non-limiting embodiment, at least 90% toabout 100% of the barrier may be removed, alternatively at least 50%,and in another non-limiting embodiment at least 10%.

A third fluid may also be used for further degrading of the metallicpowder particles. “Third fluid” is defined herein as any fluid usedafter the second fluid that may degrade the metallic powder particles ina different manner than that of the second fluid.

In the foregoing specification, the invention has been described withreference to specific embodiments thereof, and has been demonstrated aseffective in providing methods and compositions for strengthening awellbore. However, it will be evident that various modifications andchanges can be made thereto without departing from the broader spirit orscope of the invention as set forth in the appended claims. Accordingly,the specification is to be regarded in an illustrative rather than arestrictive sense. For example, specific combinations of or types ofbase fluids, metallic particle compacts, metallic particles, particlecores, metallic coating layers, second fluids, third fluids, and othercomponents falling within the claimed parameters, but not specificallyidentified or tried in a particular composition or method, are expectedto be within the scope of this invention. Further, it is expected thatthe components and proportions of the base fluid and metallic powderparticles and procedures for strengthening the wellbore or forming ametallic powder barrier at or near the fracture tip may change somewhatfrom one application to another and still accomplish the stated purposesand goals of the methods described herein. For example, the methods mayuse different pressures, pump rates, additional fluids, and/or differentsteps than those exemplified herein.

The words “comprising” and “comprises” as used throughout the claims isinterpreted “including but not limited to”.

The present invention may suitably comprise, consist or consistessentially of the elements disclosed and may be practiced in theabsence of an element not disclosed. For instance, a method forstrengthening a wellbore may consist of or consist essentially ofcontacting the wellbore with a fluid composition having a base fluid anda metallic powder having a plurality of metallic particles, and forminga metallic powder barrier at or near the tip of a fracture extendingfrom the wellbore into a subterranean formation, where the methodfurther consists of or consists essentially of degrading the metallicpowder particles after a predetermined condition, and reducingadditional growth of the fracture as compared to contacting the wellborewith a fluid composition absent the metallic powder.

What is claimed is:
 1. A method for strengthening a wellbore comprising:contacting the wellbore with a fluid composition, wherein the fluidcomposition comprises: a base fluid selected from the group consistingof a drilling fluid, a completion fluid, a servicing fluid, a fracturingfluid, and mixtures thereof; and metallic powder comprising a pluralityof metallic powder particles, each powder particle comprising: aparticle core comprising a core material having a melting temperature(T_(p)), and wherein the core material is selected from the groupconsisting of magnesium, zinc, aluminum, manganese, vanadium, chromium,molybdenum, iron, cobalt, silicon, nitride, tungsten, and a combinationthereof; and a metallic coating layer disposed on the particle core,wherein the metallic coating layer comprises a metallic coating materialhaving a melting temperature (T_(c)); and forming a first metallicpowder barrier at or near the tip of a fracture extending from thewellbore into a subterranean formation with the metallic powder.
 2. Themethod of claim 1, wherein the metallic powder particles are configuredfor solid-state sintering to one another at a predetermined sinteringtemperature (T_(s)) to form a metallic particle compact, and whereinT_(s) is less than T_(p) and T_(c).
 3. The method of claim 2, whereinthe size of the metallic particle compact ranges from about 500 μm toabout 20 cm.
 4. The method of claim 1, wherein the fluid compositioncomprises a concentration of the metallic powder in an amount rangingfrom about 0.05 wt % to about 10 wt % of the total fluid composition. 5.The method of claim 1 further comprising reducing additional growth ofthe fracture as compared to the wellbore absent the metallic powderbarrier.
 6. The method of claim 1, further comprising reducing an amountof the base fluid lost to the formation as compared to the amount offluid lost to the formation in the absence of the metallic powderbarrier.
 7. The method of claim 1, further comprising forming a secondmetallic powder barrier on the wellbore to prevent solid and fluid goingfrom or into the formation.
 8. The method of claim 1, further comprisingcontacting the metallic powder barrier with a surfactant to reverse thewettability of at least a portion of the metallic powder particlestherein.
 9. The method of claim 6, wherein the surfactant is part of amesophase fluid selected from the group consisting of a miniemulsion, ananoemulsion, a macroemulsion, and combinations thereof.
 10. The methodof claim 1 further comprising degrading at least a portion of themetallic powder barrier after a predetermined condition selected fromthe group consisting of a temperature change, the presence of an acid,an amount of time, and combinations thereof.
 11. The method of claim 8,wherein the degrading the metallic powder particles occurs by a methodselected from the group consisting of dissolving the metallic powderparticles, disintegrating the metallic powder particles, corroding themetallic powder particles, melting the metallic powder particles, andcombinations thereof.
 12. The method of claim 1, wherein the corematerial is selected from the group consisting of an Mg—Zn alloy, anMg—Al alloy, an Mg—Mn alloy, an Mg—Zn—Y alloy, and combinations thereof.13. The method of claim 1, wherein the size of the powder particleranges from about 25 nm to about 5000 μm.
 14. The method of claim 1,wherein the particle core has a diameter ranging from about 1 μm toabout 300 μm.
 15. The method of claim 1, wherein the core materialcomprises an Mg—Al—X alloy; and wherein X is selected from the groupconsisting of Zn, Mn, Si, Ca, Y, and combinations thereof.
 16. Themethod of claim 13, wherein the Mg—Al—X alloy comprises up to about 85wt % of Mg, up to about 15 wt % Al, and up to about 5 wt % X.
 17. Themethod of claim 1, wherein the metallic coating material is selectedfrom the group consisting of Al, Zn, Mn, Mg, Mo, W, Cu, Fe, Si, Ca, Co,Ta, Re, Ni, an oxide thereof, a carbide thereof, a nitride thereof, anda combination of any of the aforementioned materials; and wherein themetallic coating material has a different chemical composition than thechemical composition of the particle core.
 18. A method forstrengthening a wellbore comprising: contacting the wellbore with afluid composition, wherein the fluid composition comprises: a base fluidselected from the group consisting of a drilling fluid, a completionfluid, a servicing fluid, a fracturing fluid, and mixtures thereof; anda metallic powder comprising a plurality of metallic powder particles,each powder particle comprising: a particle core comprising a corematerial having a melting temperature (T_(p)), and wherein the corematerial is selected from the group consisting of magnesium, zinc,aluminum, manganese, vanadium, chromium, molybdenum, iron, cobalt,silicon, nitride, tungsten, and a combination thereof; and a metalliccoating layer disposed on the particle core, wherein the metalliccoating layer comprises a metallic coating material having a meltingtemperature (T_(c)); and wherein the metallic powder particles areconfigured for solid-state sintering to one another at a predeterminedsintering temperature (T_(S)), and T_(S) is less than T_(P) and T_(C) toform a metallic particle compact; and forming a metallic powder barrierwith the metallic powder at or near the tip of a fracture extending fromthe wellbore into a subterranean formation to reduce additional growthadditional growth of the fracture as compared to the fracture in theabsence of the metallic powder barrier; and degrading at least a portionof the metallic powder barrier after a predetermined condition selectedfrom the group consisting of a temperature change, the presence of anacid, an amount of time, and combinations thereof.
 19. A method forstrengthening a wellbore comprising: contacting the wellbore with afluid composition, wherein the fluid composition comprises: a base fluidselected from the group consisting of a drilling fluid, a completionfluid, a servicing fluid, a fracturing fluid, and mixtures thereof; anda metallic powder comprising a plurality of metallic powder particlesranging in size from about 25 nm to about 5000 nm, each powder particlecomprising: a particle core comprising a core material having a meltingtemperature (T_(p)), and wherein the core material is selected from thegroup consisting of magnesium, zinc, aluminum, manganese, vanadium,chromium, molybdenum, iron, cobalt, silicon, nitride, tungsten, and acombination thereof; and a metallic coating layer disposed on theparticle core, wherein the metallic coating layer comprises a metalliccoating material having a melting temperature (T_(c)); and forming ametallic powder barrier at or near the tip of a fracture extending fromthe wellbore into a subterranean formation with the metallic powder;contacting the metallic powder barrier with a surfactant to reverse thewettability of at least a portion of the metallic powder particlestherein.